Some hatchback doors, sliding doors, and the like of vehicles can be opened and closed by door opening/closing devices besides by a manual opening and closing operation (refer to Patent Literature 1, for example). Some of the door opening/closing devices assist the manual opening and closing operation, thereby reducing an operator's burden. Such door opening/closing devices cause a control unit to perform pulse-width modulation (PWM) control on the rotation rate of a motor, thereby moving the door in an opening direction or a closing direction.